Fig. 6

Group structures of the glass assemblage from the Forum of Caesar. a TiO₂O/Al₂O₃ and Al₂O₃/SiO₂ ratios and b Sb versus Mn distinguish different base glass types. Lines indicate the thresholds below which Mn (< 250 ppm) and Sb (< 30 ppm) may be considered natural impurities of the raw materials; c the tesserae from the forum compared to reference groups from the Iulia Felix shipwreck [53] and Roman tesserae from West Clacton [54] (N. Schibille)